Arturia 2.6 manual Filter or VCF

The complete cycle of a wave form (sawtooth) = one period

Oscillator synchronization: the second is synchronized on the first one

In the image above, oscillator2 is synchronized with the first, and then tuned to a frequency with double the tonality.

The noise module: the noise signal spectrum possesses all frequencies at the same volume. For this reason, the noise module is used to create different noises like the imitation of wind or a breath, or even special effects. White noise is the richest of noises. Pink noise is also commonly present on synthesizers. It is not as rich in high frequencies as white noise, having received a low pass filtering.

Also, note that the audio output of the noise can be used as a modulation signal (specially when it is heavily filtered) to create random cyclic variations.

On pre-cabled synthesizers, the noise module is either integrated into the oscillator, (its audio output being placed as a complement on top of the wave form outputs) or the mixer directing the signals to the filter. On the other hand, on modular synthesizers, it is an independent module.

8.1.2The filter or VCF

The audio signal generated by an oscillator (the wave form) is generally directed towards a filter module (Voltage Controlled Filter). It is this module that allows the modeling of the sound by filtering (by subtraction, explaining the name of this type of synthesis) the harmonics situated around a cut-off frequency. It can be considered like a sophisticated equalizer, which reduces, depending on the case, the low or high frequencies of a sound.

The removal of unwanted frequencies from a cut-off frequency is not sudden, but is done progressively, depending on the filter slope. This filter slope is expressed in dB/octave. The filters used in classic analog synthesizers have slopes of 24 dB/octave or 12 dB/octave.

The 24 dB/octave offers a more efficient filtering than the 12 dB/octave.

102 ARTURIA – MOOG MODULAR V 2.6 – USER’S MANUAL